1. Technical Field
The present invention relates to an oscillation circuit, an oscillator, a method of manufacturing an oscillator, an electronic device, and a moving object.
2. Related Art
In a resonator such as a quartz crystal resonator (piezoelectric resonator) or a micro electro mechanical systems (MEMS) resonator, characteristics of the resonator are required to be inspected by performing an overdrive inspection in which an alternating current (AC) signal of a high current, voltage, or power is applied and the resonator is driven to thereby inspect frequency characteristics of the resonator, a drive level characteristic inspection in which a signal obtained by increasing and decreasing an AC signal of a high current, voltage, or power is applied in a stepwise manner and the resonator is driven to thereby inspect a fluctuation in the frequency characteristics of the resonator, or the like.
On the other hand, the development has been performed of an oscillator in which a quartz crystal resonator and an oscillation circuit are accommodated in the same accommodation container, in order to achieve a reduction in the size of the oscillator. For this reason, various devices have been performed in order to inspect characteristics of a resonator after the quartz crystal resonator and the oscillation circuit are mounted within the same accommodation container.
JP-A-2009-201097 discloses a quartz crystal oscillator capable of being miniaturized by causing a functional terminal of an oscillator to double as an inspection terminal of a quartz crystal resonator, as compared with a case where an inspection terminal is independently provided.
However, in the quartz crystal oscillator disclosed in JP-A-2009-201097, a high voltage may be applied between both ends of a variable capacitive element embedded in an oscillation circuit, for example, during an overdrive inspection or a drive level inspection, which results in a concern that the variable capacitive element may be damaged. In particular, in an oscillator in which a frequency changes depending on a control voltage, a variable capacitive element may be realized using an MOS having a thin gate oxide film or a small size L in order to increase a voltage sensitivity of a frequency (the amount of change in a frequency with respect to the amount of change in a control voltage). Such a variable capacitive element has a low ability to withstand pressure, and thus there is a tendency for the element to be damaged when a high voltage is applied to both ends thereof. Alternatively, there is a tendency for a service time to be decreased. This problem is not limited to the variable capacitive element and similarly occurs also in a capacitive element having a fixed capacitance value or various types of electronic elements such as an inductor.